Assessing the Effectiveness of Air-assisted and Hydraulic Sprayers in Cotton Via Leaf Bioassay

Compared with conventional over-the-top sprayers, air-assisted and drop-nozzle sprayers should provide improved pesticide penetration and coverage within the plant canopy where the insects feed. This study compared the effectiveness of the insecticide Tracer, a natural insecticide produced by the actinomycete Saccharopolyspora spinosa, (Dow Agrosciences, Indianapolis, IN) applied by these three sprayers within the canopy of cotton (Gossypium hirsutum L.). Leaves from the top, middle, and bottom of cotton plants were used in a bioassay as an indicator of insecticide deposition within the canopy. The test measured the mortality of beet armyworm (Spodoptera exigua, Hübner) larvae feeding on the sampled leaves. All three sprayers provided adequate coverage for good insect control in the top of the cotton canopy. The air-assisted sprayer provided the best insect mortality throughout the canopy, while the over-the-top sprayer had the poorest insect mortality in the bottom. Air-assisted and drop-nozzle sprayers provided good insect mortality in the middle of plants.